Linear scanning array with adjustable polarizers and hybrids in the coupling network



May 20, I969 LINEAR SCANNING ARRAY WITH ADJUSTABLE FCLARIZERS HYBRIDS IN THE COUPLING NETWORK Filed Jan. 12, 1966 TO TRANSMITTER L. HATKIN 3,445,853

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LEONARD HATKIN ATTORNEYS United States Patent U.S. Cl. 343-854 5 Claims ABSTRACT OF THE DISCLOSURE An electronic scanning antenna array including a plurality of antenna elements disposed in spaced substantially aligned relation with a reference antenna and symmetrically arranged therewith, and further including for each pair of symmetrically arranged antennas an RF polarization rotator adapted to provide two orthogonal RF outputs which are fed to an associated antenna pair through a hybrid Magic-T waveguide. The sum (2) arm of the Magic-T is fed one orthogonal RF output and the difference arm (A) of the Magic-T is fed the other orthogonal output through a 90 phase shifter, and each of the symmetrical antenna pairs is fed through the respective side arms of the Magic-T.

This invention relates to antenna directive systems and more particularly to such systems utilizing directional beams of microwave or radio-frequency energy, or radiating patterns, which may be varied in direction or scanned.

It is well known that in order to scan the beam radiated from a linear antenna array, it is necessary to vary the phase of the elements of the array so that each element has a constant differential phase shift with respect to the previous one. The direction of the radiated beam may be steered or scanned by varying the differential phase shift, or, so that the beam will point towards the lagging phase elements in a direction 0 =sinwhere K=21r/ and d is the element spacing. Thus, by varying 0c the direction of beam pointing may be changed. Heretofore, the phase between antenna elements was changed either by varying the operating frequency or by utilizing phase shifters in a series or parallel arrangement. Such systems present problems inasmuch as frequency variation consumes bandwidth, and requires a bulky antenna and complex transmitter. Also, use of phase shifters requires at least one phase shifter per element.

It is an object of the present invention to provide a scanning array wherein the above mentioned problems are overcome.

It is another object of the present invention to provide an electronic scanning antenna array having a reduced number of control devices per radiating element and adapted to be operated by means of a simplified master control.

In accordance with the present invention, there is provided an antenna array which includes a plurality of antenna elements disposed in spaced substantially aligned relation. Also included are discrete means for controlling the RF energy fed to the antenna elements for varying the relative phase difference between the elements of the array and simultaneously maintaining constant the amplitude at each antenna element.

For a better understanding of the invention, together with further objects thereof, reference is made to the following description taken in connection with the accompanying drawing wherein the single figure is a schematic representation of the present invention.

Referring now to the drawing, there is shown at 10 an antenna array comprising a number of radiating elements 11, 13, 15, 17 and 19, regularly spaced with respect to each other and in substantially aligned relation. Each successive element is to be fed with the energy to be radiated, the magnitude of energy fed to one such element being proportional to a coefficient of a prescribed expansion, for example binomial, well known in the art to provide reduced side lobes. Considering now' the center antenna element 15 as the reference antenna, the energy to be radiated is fed directly from the transmitter (not shown) to reference antenna 15 through a suitable circular waveguide as at 21. The outer symmetrically arranged antennas 11 and 19, and the inner symmetrically arranged antennas 13 and 17, are fed energy to be radiated through respective control circuits hereinbelow described.

Each of the feed control circuits shown at 25 and 45, respectively, include a radio-energy polarization rotation device and a hybrid Magic-T circuit. Referring now to control circuit 25 which feeds inner antennas 13 and 17, at 27 there is shown a circular Waveguide having two orthogonally arranged pick-offs or output terminals 29 and 31, and in which the linear polarized vector E is rotated. The linear polarized frequency energy E is fed to circular waveguide 27 from the transmitter, with the Waveguide 27 being adapted to propagate the TE mode. The polarization rotation may be accomplished mechanically by means of a rotating half-wave plate within the waveguide 27 or electronically by means of a ferrite Faraday rotation or other suitable device. Both methods are so well known in the art that no further description thereof is believed necessary. As shown, the energy derived from the orthogonally arranged pick-offs or output terminals 29 and 31 are applied as respective inputs to a waveguide Magic-T33. Assuming B is the angle the polarization vector E makes with one of the output terminals, 29 for example, then the output terminals 29 and 31 will be proportional to cos [3 and sin 3 respectively. The cos [9 output from terminal 29 is fed to the sum (2) arm of waveguide Magic-T 33 and the sin [9 output is fed from terminal 31 through a differential phase shift by means of phase shifter 35 to the difference (A) arm of waveguide Magic-T 33. The outputs from side arms SA, and 8A of waveguide Magic-T 33 are applied, respectively, to antennas 13 and 17. It can be shown that the side arm outputs SA and 8A are conjugates so that the radio frequency energy to be radiated by antenna .13 is 707E43 while that radiated by antenna 17 is .7O7E4-B It is to be understood of course that any other suitable hybrid waveguide having a sum and difference arm may be used in place of the Magic-T.

The control system for antennas 11 and 19 is shown at 45 and includes the identical components of control element 25. That is, waveguide 47, terminals 49 and 51, Magic-T 53 and phase shifter 55 correspond to identical elements 27, 29, 31, 33 and 35 of control circuit 25. However, the angle of rotation, {3 in Waveguide 47 will be twice that of the angle of rotation of p, in waveguide 27. Thus, assuming that B =oc, then 5 :20:. With the arrangement hereinabove described, it can be seen that the phases of the elements of a pair of symmetrically located antenna elements are +,8 and -/3, respectively. If ,B is varied, the relative phase difference between the elements of the array changes, but the amplitude at each element remains constant. Of course, the amplitude across the array may be symmetrically tapered by tapering the inputs to each control device. Also, since the angle of rotation of polarization in each control device is an integral multiple of the angle in the first control device,

i.e., :0; and fi =2a, the control device may be ganged mechanically or electrically and thus operated from a central control. Thus, choosing the proper value of 3 points the beam in a required direction 0 While the present invention has been described as having five antenna elements, it is to be understood that it is not to be limited thereto. For example, if seven antenna elements comprised the array, then a third control device would be needed and the angle of rotation of the linear polarization 8 304. Thus, with the above described antenna systems, it can be seen that substantially half as many control elements are required as compared to the number of antenna elements.

What is claimed is:

1. An antenna array comprising a central reference antenna, a plurality of uniformly spaced paired antenna elements disposed in substantially aligned relationship with said reference antenna and symmetrically arranged therewith, and discrete RF energy feed control means each comprising a linear RF energy polarization rotator, a 90 degree difierential phase shifter, and a hybrid waveguide in circuit with each pair of antenna elements symmetrically arranged with respect to said reference antenna.

2. The antenna array as set forth in claim 1 wherein each of said polarization rotators include means for producing outputs proportional to the cosine and sine of the angle of polarization.

3. The antenna array as set forth in claim 2 wherein each of said hybrid waveguides comprise a Magic-T Waveguide.

4. The antenna array as set forth in claim 1 wherein each RF linear polarization rotator has two orthogonal output terminals, and each hybrid waveguide has a sum arm, a difference arm, and two side arms, the rotated RF energy being applied from one of said orthogonal output terminals directly to said sum arm, and to said difference arm from the other of said output terminals through said degree differential phase shifter, the respective outputs of the side arm being applied to said respective paired antenna elements.

5. The antenna array as set forth in claim 4 wherein the RF polarization angle in the rotator feeding the symmetrical antenna element pair closest to said reference antenna is at a prescribed angle, and the respective polarization angles in the rotators feeding successively more distant antenna element pairs are successive increasing integral multiples of said prescribed angle.

References Cited UNITED STATES PATENTS 2,286,839 6/1942 Schelkunolf 343853 3,135,960 6/1964 Kaiser 343895 X 3,255,450 6/1966 Butler 343853 3,267,472 7/1966 Fink 343854 ELI LIEBERMAN, Primary Examiner.

US. Cl. X.R. 333-11 

